Melt-spun multifilament polyolefin yarn formation processes and yarns formed therefrom

ABSTRACT

Disclosed is a method of forming multifilament polyolefin yarns and yarns formed according to the disclosed method. The yarns can be polypropylene yarns and can exhibit any of a high modulus, high tenacity, and a unique crystalline structure for multifilament polyolefin yarns. The process can generally include extruding a polymeric melt including the polyolefin at a relatively high throughput and low spinline tension and quenching the filaments in a liquid bath prior to drawing the fiber bundle at a relatively high draw ratio, for example greater than 10, in some embodiments.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 10/983,153 having a filing date of Nov. 5, 2004,now U.S. Pat. No. 7,074,483.

BACKGROUND OF THE INVENTION

Yarns and fibers formed from polyolefins can offer many desirablecharacteristics. For example, they can possess good tactile qualitiessuch as hand feel, they can be resistant to degradation and erosion, andthe raw materials can be easy to obtain as well as fairly inexpensive.As such, monofilament fibers as well as multifilament yarns have beenformed from various polyolefins such as polypropylene. While thedevelopment of monofilament polyolefin fibers that have high modulus andhigh tenacity has been achieved, the ability to produce high modulus,high tenacity multifilament yarns of similar materials has not been assuccessful. As such, there remains room for improvement and variationwithin the art.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is directed to a method offorming a polyolefin multifilament yarn. For example, the method caninclude forming a melted polymeric composition including a polyolefin,extruding the composition to form multiple filaments, quenching thefilaments in a liquid bath, collecting the filaments to form a fiberbundle, and drawing the fiber bundle in a heated drawing step with adraw ratio greater than about 6, and in one embodiment, greater thanabout 10.

The polyolefin can be any polyolefin suitable for forming yarn. Forexample, the polyolefin can be a copolymer. In one embodiment, thepolyolefin can be a polypropylene. Optionally, the yarn can be formed ofa mixture of two or more polyolefins. In one embodiment, the polyolefincan have a melt flow index between about 0.2 and about 50.

In one embodiment, the polypropylene can contain a nucleating agent. Forexample, the nucleating agent can be a dibenzylidene sorbitol nucleatingagent as is generally known in the art. Generally, the nucleating agentcan be present in the melt in an amount less than about 1% by weight ofthe extruded composition, though this is not a requirement of theinvention.

The extruder can generally be any standard multi-orifice extruder. Forexample, the extruder can define multiple orifices, and each orifice canhave a maximum cross-sectional dimension of between about 0.001 andabout 0.050 inches.

The melt can be extruded fairly slowly, for example between about 1m/min and about 25 m/min into the liquid quench bath. Optionally, thebath can be heated, such as to a temperature of between about 50° C. andabout 130° C. In one embodiment, the surface of the quench bath can bequite close to the extruder orifices, for example within the distance ofthe die swell of the filaments. In another embodiment, the areaimmediately downstream of the orifice can be protected by a heated or anunheated gaseous shroud.

The heated drawing step can be carried out in an oven, utilizing heateddrawing rolls, or according to any other suitable heating method.Generally, the heated drawing step can be carried out at a temperatureof between about 80° C. and about 170° C. For example, the oven or thedrawing rolls can be heated to the desired temperature. The heateddrawing step can also be carried out at an even higher temperature if,for example, the yarn is exposed to the heat for a very short period oftime.

Other processes can also be carried out in forming the disclosedmultifilament yarn such as one or more of the following: application ofa lubricant, a second draw, or heat setting of the yarn.

In another embodiment, the invention is directed to yarn that can beformed according to the disclosed processes. For instance, the yarn caninclude multiple filaments that can each describe a denier of less thanabout 300, in one embodiment each filament can have a denier of betweenabout 0.5 and about 100. The yarn can have a high modulus, for instancegreater than 40 g/d. In another embodiment, the yarn can have a modulusgreater than 100 g/d, or greater than 150 g/d in some embodiments. Theyarn can also have a high tenacity, for example greater than about 5 g/din some embodiments, and greater than about 7 g/d in other embodiments.The disclosed yarns can also be fairly resistant to stretching, forexample, the yarn can exhibit an elongation of less than about 10%.

The disclosed yarn is also believed to possess a crystalline structurethat is unique for multifilament polyolefin yarn. For instance, at leastone of the filaments in the yarn can possess greater than 80%crystallinity, according to known wide-angle x-ray scattering (WAXS)measuring techniques. In one embodiment, at least one of the filamentsin the yarn can have a ratio of equatorial intensity to meridonalintensity greater than about 1.0, which can be obtained from known smallangle x-ray scattering (SAXS) measuring techniques. In anotherembodiment, the ratio of equatorial intensity to meridonal intensity canbe greater than about 3.0.

In one embodiment, the invention is directed to secondary products thatcan be formed and can include the disclosed yarns. For example, thedisclosed yarn can be beneficially utilized in forming ropes, wovenmaterials, and nonwoven materials.

In one embodiment, the disclosed yarn can be utilized in reinforcementmaterials, for instance reinforcement materials for use in reinforcing ahydratable cementitious composition. For example, a yarn formedaccording to the disclosed processes can be chopped into smaller pieces,generally less than about 5 inches, to form a reinforcement material. Inone embodiment, the yarn can be chopped into pieces of less than about 3inches in length. In another embodiment, it can be chopped into piecesof less than about 1 inch in length. Optionally, the reinforcementmaterials can be degraded and/or deformed in addition to being cut intosmaller pieces.

BRIEF DESCRIPTION OF THE FIGURES

A full and enabling disclosure of the present invention, including thebest mode thereof, to one of ordinary skill in the art, is set forthmore particularly in the remainder of the specification, includingreference to the accompanying Figures in which:

FIG. 1 illustrates one embodiment of a process according to the presentinvention;

FIG. 2 illustrates the die swell of a single filament formed accordingto one embodiment of the present invention;

FIG. 3 is the WAXS scattering pattern of a polypropylene filament pulledfrom a multifilament yarn formed according to one embodiment of thepresently disclosed processes; and

FIG. 4 is the SAXS scattering pattern of the polypropylene filament ofFIG. 3.

Repeat use of reference characters in the present specification anddrawings is intended to represent the same or analogous features orelements of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to various embodiments of theinvention, one or more examples of which are set forth below. Eachembodiment is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment, can be used in another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncover such modifications and variations as come within the scope of theappended claims and their equivalents.

In general, the present invention is directed to multifilamentpolyolefin yarns and methods suitable for forming the disclosedmultifilament polyolefin yarns. Beneficially, the disclosed methods canbe utilized to form multifilament polyolefin yarns that can exhibit atleast one of higher modulus or higher tenacity as compared to previouslyknown multifilament polyolefin yarns.

The methods of the disclosed invention are generally directed to amelt-spinning yarn formation process. More particularly, the processutilized in forming the disclosed yarns can include forming a moltencomposition including a polyolefin, extruding multiple (i.e., at leastthree) individual filaments of the composition at a relatively lowspinning rate, quenching the filaments in a liquid, forming a yarnstructure of the multiple individual filaments, and mechanically drawingthe yarn structure while the structure is heated.

In one particular embodiment, the polyolefin utilized in forming thedisclosed yarns can be a polypropylene. This is not a requirement of thepresent invention, however, and though the ensuing discussion isgenerally directed toward polypropylene, it should be understood thatother polyolefins can optionally be utilized in the invention. Forexample, in one embodiment, the disclosed invention can be directed tothe formation of polyethylene or polybutylene multifilament yarn.

In addition, and for purposes of this disclosure, the term polypropyleneis intended to include any polymeric composition comprising propylenemonomers, either alone (i.e., homopolymer) or in mixture or copolymerwith other polyolefins, dienes, or other monomers (such as ethylene,butylene, and the like). The term is also intended to encompass anydifferent configuration and arrangement of the constituent monomers(such as syndiotactic, isotactic, and the like). Thus, the term asapplied to fibers is intended to encompass actual long strands, tapes,threads, and the like, of drawn polymer.

For purposes of this disclosure, the terms fiber and yarn are intendedto encompass structures that exhibit a length that far exceeds theirlargest cross-sectional dimension (such as, for example, the diameterfor round fibers). Thus, the term fiber as utilized herein differs fromstructures such as plaques, containers, sheets, and the like that areblow-molded or injection molded. Moreover, the term multifilament yarnis intended to encompass a structure that includes at least threefilaments that have been individually formed such as, for example, viaextrusion through a spinneret, prior to being brought in proximity toone another to form a single yarn structure.

One embodiment of the presently disclosed process generally 10 isschematically illustrated in FIG. 1. According to the illustratedembodiment, a polymeric composition can be provided to an extruderapparatus 12. For example, in one embodiment, the polymeric compositioncan include polypropylene.

Generally, any polypropylene suitable for forming drawn yarn can beutilized in the disclosed process. For instance, polypropylene suitablefor the present invention can generally be of any standard melt flow.For example, in one embodiment, standard extrusion grade polypropyleneresin possessing ranges of melt flow indices (MFI) between about 0.2 andabout 50 can be utilized in forming the disclosed multifilament yarns.In one embodiment, polypropylene possessing an MFI between about 0.5 andabout 25 can be utilized. In one embodiment, the polypropylene utilizedin forming the multifilament yarn can have an MFI between about 1 andabout 15.

In one embodiment, the polymeric composition provided to the extruderapparatus 12 can include polypropylene and a nucleating agent. Accordingto this embodiment, the nucleating agent can generally be any materialthat can provide nucleation sites for the polypropylene crystals thatcan form during the transition of the polypropylene from the moltenstate to the solid structure. In one embodiment, the nucleating agentcan exhibit high solubility in the polypropylene, though this is not arequirement of the invention. A non-limiting list of exemplarynucleating agents can include, for example, dibenzylidene sorbitolnucleating agents, as are generally known in the art, such asdibenzylidene sorbitol (DBS), monomethyldibenzylidene sorbitols such as1,3:2,4-bis(p-methylbenzylidene) sorbitol (p-MDBS), dimethyldibenzylidene sorbitols such as 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (3,4-DMDBS), and the like. Other suitable nucleating agents caninclude sodium benzoate, phosphate ester salts, such as NA-11 and NA-21,developed by Asahi Denka of Japan, or the hyper nucleating agentsdeveloped by Milliken Chemical of South Carolina such as, for example,Hyperform® HPN-68L.

According to the disclosed process, the polymeric composition, whichcan, in one embodiment include polypropylene combined with a nucleatingagent, can be provided to an extruder apparatus 12. In this particularembodiment, the polypropylene component and the nucleating agent can beprovided to the extruder apparatus 12 either separately or together, asat an inlet 13. For example, polypropylene and a nucleating agent can beprovided to the extruder 12 either separately or together in liquid,powder, or pellet form. For instance, in one embodiment, both thepolypropylene and the nucleating agent can be provided to the extruder12 in pellet form at inlet 13. In another embodiment, the nucleatingagent can be provided to the extruder apparatus 12 in a liquid form. Forexample, nucleating agents in a liquid form such as those disclosed inU.S. Pat. No. 6,102,999 to Cobb, III. et al., which is incorporatedherein by reference, can be utilized in the process.

When included, the nucleating agent can generally be present in themixture to be extruded in an amount less than about 1% by weight of thecomposition. For example, the nucleating agent can be present in themixture in an amount less than about 0.5% by weight. In one embodiment,the nucleating agent can be present in the mixture in an amount betweenabout 0.01% by weight and about 0.3% by weight. In another embodiment,the nucleating can be present in the mixture in an amount between about0.05% by weight and about 0.25% by weight.

The mixture including the polypropylene and, optionally, the nucleatingagent can also include various other additives as are generally known inthe art. For example, in one embodiment, the disclosed multifilamentyarn can be colored yarn, and the mixture can include suitable coloringagents, such as dyes or other pigments. According to this embodiment, itmay be preferable to utilize a nucleating agent that will not affect thefinal color of the multi-component yarn, but this is not a requirementof the invention, and in other embodiments, nucleating agents can beutilized that enhance or otherwise affect the color of the formed yarn.Other additives that can be combined with the mixture can include, forexample, one or more of anti-static agents, antioxidant agents,antimicrobial agents, adhesion agents, stabilizers, plasticizers,brightening compounds, clarifying agents, ultraviolet light stabilizingagents, surface active agents, odor enhancing or preventative agents,light scattering agents, halogen scavengers, and the like. In addition,additives can be included in the melt, or in some embodiments, can beapplied as a surface treatment to either the undrawn fiber bundle oroptionally to the drawn yarn, as generally known in the art.

In one embodiment, the extruder apparatus 12 can be a melt spinningapparatus as is generally known in the art. For example, the extruderapparatus 12 can include a mixing manifold 11 in which a compositionincluding one or more polyolefins and any other desired additives can bemixed and heated to form a molten composition. The formation of themolten mixture can generally be carried out at a temperature so as toensure melting of essentially all of the polypropylene. For example, inone embodiment, the mixture can be mixed and melted in a manifold 11heated to a temperature of between about 175° C. and about 325° C.

Optionally, to help ensure the fluid state of the molten mixture, in oneembodiment, the molten mixture can be filtered prior to extrusion. Forexample, the molten mixture can be filtered to remove any fine particlesfrom the mixture with a filter of between about 180 and about 360 gauge.

Following formation of the molten mixture, the mixture can be conveyedunder pressure to the spinneret 14 of the extruder apparatus 12, whereit can be extruded through multiple spinneret orifices to form multiplefilaments 9. For instance, the spinneret can define at least threespinneret orifices. In one embodiment, the spinneret can define between4 and about 100,000 individual spinneret orifices. For purposes of thisdisclosure, the terms extrusion die and spinneret are used hereininterchangeably and intended to mean the same thing; the same is truefor the terms spinneret orifice, spinneret aperture, extruder orificeand extruder aperture. The spinneret 14 can generally be heated to atemperature that can allow for the extrusion of the molten polymer whilepreventing breakage of the filaments 9 during formation. For example, inone embodiment, the spinneret 14 can be heated to a temperature ofbetween about 175° C. and about 325° C. In one embodiment, the spinneret14 can be heated to the same temperature as the mixing manifold 11. Thisis not a requirement of the process, however, and in other embodiments,the spinneret 14 can be at a different temperature than the mixingmanifold 11.

The spinneret orifices through which the polymer can be extruded cangenerally be less than about 0.1 inches in maximum cross-sectionaldistance (e.g., diameter in the particular case of a circular orifice).For example, in one embodiment, the spinneret orifices can be betweenabout 0.002 inches and about 0.050 inches in maximum cross-sectionaldistance.

According to the present invention, the polymer can be extruded throughthe spinneret at a relatively high throughput. For example, the polymercan be extruded through the spinneret at a throughput of not less thanabout 50% of that required to give melt fracture. In other words, thethroughput can be at least 50% of the throughput at which the moltenexudate can become excessively distorted. The specific melt fracturethroughput can generally vary depending upon one or more of the exudatematerial, the total number of apertures in the spinneret, the spinneretaperture size, as well as the exudate temperature. For example, whenconsidering the extrusion of molten polypropylene through a spinneret of8 round apertures of 0.012-inch diameter each, melt fracture can occurat a pump speed of between about 22 and about 24 revolutions/minute of a0.160 cm³/rev melt pump, or a throughput of about 5.5-6.0 g/min, whenextruding a 4 melt flow homopolymer polypropylene at a spinnerettemperature of about 230° C. Specific melt fracture throughput valuesfor any particular system and materials as well as methods of obtainingsuch are generally known to those of skill in the art, and thus adetailed discussion of this phenomenon is not included herein.

In addition to a relatively high throughput, the filaments can also beformed at a relatively low spinline tension. The combination of highthroughput with low spinline tension can allow the filaments to beformed with a relatively low ratio of orifice size to final drawnfilament size as compared to other previously known multifilamentformation processes. For instance, the ratio of the maximumcross-sectional width of an orifice to the maximum cross-sectionaldistance of a single fully drawn filament extruded through the orificecan, in one embodiment, be between about 2 and about 10. In oneembodiment, this ratio can be between about 3 and about 8. Accordingly,the material forming each filament can be in a fairly relaxed,disorganized state as it begins to cool and crystallize.

Referring again to FIG. 1, following extrusion of the polymer, theun-drawn filaments 9 can be quenched in a liquid bath 16 and collectedby a take-up roll 18 to form a multifilament fiber structure or fiberbundle 28. While not wishing to be bound by any particular theory, it isbelieved that by extruding the filaments at a relatively low spinlinetension and high throughput combined with quenching the polymericfilaments in a liquid bath, the presently disclosed process encouragesthe formation of folded chain crystals in a highly disordered state inthe polymer, which in turn enables a high draw ratio to be utilized inthe process and thereby enables the formation of a multifilament yarnhaving high tenacity and modulus.

As is generally known in the art, polymers that are crystallized from amelt under dynamic temperature and stress conditions crystallize withthe rate of crystallization dependent upon both the number of nucleationsites as well as on the growth rate of the polymer. Moreover, both ofthese factors are in turn related to the conditions that the polymer issubject to as it is quenched. In addition, polymers that crystallizewhen in a highly oriented state tend to have limited tenacity andmodulus as evidenced by the limited draw ratios possible for such highlyoriented polymers. Thus, in order to obtain a multifilament yarn withhigh tenacity and modulus, i.e., formed with a high draw ratio,crystallization of the polymer while in a highly disordered state issuggested. Accordingly, the present invention discloses a multifilamentyarn formation process in which crystallization of the polymer in ahighly disordered state is promoted by encouraging the filament tomaximize its relaxation into the desired disoriented state duringcrystallization by forming the polymer at a relatively high throughputand low spinline tension. Optionally, a higher rate of crystallizationcan also be encouraged in certain embodiments through addition of anucleating agent to the melt. In addition, quenching the formed polymerfilaments in a liquid bath can promote the formation of folded chaincrystals, which is also associated with the high draw ratios of hightenacity, high modulus materials.

As described, the individual filaments 9 can be extruded according tothe disclosed process at relatively low spinline tension. As such, thetake-up roll 18 can operate at a relatively low speed. For example, thetake-up roll 18 can generally be set at a speed of less than about 25meters per minute (m/min). In one embodiment, the take-up roll 18 can beset at a speed of between about 1 m/min and about 20 m/min.

The liquid bath 16 in which the filaments 9 can be quenched can be aliquid in which the polymer is insoluble. For example, the liquid can bewater, ethylene glycol, or any other suitable liquid as is generallyknown in the art. In one embodiment, in order to further encourage theformation of folded chain crystals in the filaments 9, the bath 16 canbe heated. For example, the bath can be heated to a temperature near themaximum crystallization temperature (T_(c)) of the polymer. For example,the bath can be heated to a temperature of between about 50° C. andabout 130° C.

Generally, in order to encourage formation of filaments withsubstantially constant cross-sectional dimensions along the filamentlength, excessive agitation of the bath 16 can be avoided during theprocess.

In one embodiment, quenching of the polymer can begin as soon aspossible following exit from the spinneret, in order to encouragecrystallization of the polymer while in the highly disoriented, relaxedstate immediately following extrusion. For example, in one embodiment,the surface of the bath 16 can be located at a minimum distance from thespinneret 14. For instance, in the embodiment illustrated in FIG. 2, thesurface of the bath 16 can be at a distance from the spinneret 14 suchthat an extruded filament 9 can enter the bath 16 within the distance ofthe die swell 31 of the filament 9. Optionally, the individual filaments9 can pass through a heated or a non-heated shroud prior to entering thebath 16. For example, a heated shroud may be utilized in thoseembodiments where the distance between the orifice and the bath surfaceis greater than the die swell. In one embodiment, the distance betweenthe spinneret and the bath can be less than 2 inches. In anotherembodiment, this distance can be less than 1 inch.

Take-up roll 18 and roll 20 can be within bath 16 and convey individualfilaments 9 and fiber bundle 28 through the bath 16. Dwell time of thematerial in the bath 16 can vary, depending upon particular materialsincluded in the polymeric material, particular line speed, etc. Ingeneral, filaments 9 and subsequently formed fiber bundle 28 can beconveyed through bath 16 with a dwell time long enough so as to ensurecomplete quench, i.e., crystallization, of the polymeric material. Forexample, in one embodiment, the dwell time of the material in the bath16 can be between about 6 seconds and about 1 minute.

At or near the location where the fiber bundle 28 exits the bath 16,excess liquid can be removed from the fiber bundle 28. This step cangenerally be accomplished according to any process known in the art. Forexample, in the embodiment illustrated in FIG. 1, the fiber bundle 28can pass through a series of nip rolls 23, 24, 25, 26 to remove excessliquid from the fiber bundle. Other methods can be alternativelyutilized, however. For example, in other embodiments, excess liquid canbe removed from the fiber bundle 28 through utilization of a vacuum, apress process utilizing a squeegee, one or more air knives, and thelike.

In one embodiment, a lubricant can be applied to the fiber bundle 28.For example, a spin finish can be applied at a spin finish applicatorchest 22, as is generally known in the art. In general, a lubricant canbe applied to the fiber bundle 28 at a low water content. For example, alubricant can be applied to the fiber bundle 28 when the fiber bundle isat a water content of less than about 75% by weight. Any suitablelubricant can be applied to the fiber bundle 28. For example, a suitableoil-based finish can be applied to the fiber bundle 28, such as LurolPP-912, available from Ghoulston Technologies, Inc. Addition of afinishing or lubricant coat on the yarn can, in some embodiments of theinvention, improve handling of the fiber bundle during subsequentprocessing and can also reduce friction and static electricity build-upon the yarn. In addition, a finish coat on the yarn can improve slipbetween individual filaments of the yarn during a subsequent drawingprocess and can increase the attainable draw ratio, and thus increasethe modulus and tenacity of the drawn multifilament yarn formedaccording to the disclosed process.

After quenching of the fiber bundle 28 and any optional process steps,such as addition of a lubricant for example, the fiber bundle can bedrawn while applying heat. For example, in the embodiment illustrated inFIG. 1, the fiber bundle 28 can be drawn in an oven 43 heated to atemperature of between about 80° C. and about 170° C. Additionally, inthis embodiment, the draw rolls 32, 34 can be either interior orexterior to the oven 43, as is generally known in the art. In anotherembodiment, rather than utilizing an oven as the heat source, the drawrolls 32, 34 can be heated so as to draw the yarn while it is heated.For example, the draw rolls can be heated to a temperature of betweenabout 80° C. and about 170° C. In another embodiment, the yarn can bedrawn over a hotplate heated to a similar temperature (i.e., betweenabout 80° C. and about 170° C.). In one embodiment, the oven, drawrolls, hotplate, or any other suitable source of heat can be heated to atemperature of between about 120° C. and about 150° C.

According to the disclosed process, the multifilament fiber bundle canbe drawn in a first (or only) draw at a high draw ratio, higher thanthose attainable in previously known polyolefin melt-spun multifilamentyarn formation processes. For example, the fiber bundle 28 can be drawnwith a draw ratio (defined as the ratio of the speed of the second orfinal draw roll 34 to the first draw roll 32) of greater than about 6.For instance, in one embodiment, the draw ratio of the first (or only)draw can be between about 6 and about 25. In another embodiment, thedraw ratio can be greater than about 10, for instance, greater thanabout 15. Additionally, the yarn can be wrapped on the rolls 32, 34 asis generally known in the art. For example, in one embodiment, betweenabout 5 and about 15 wraps of the yarn can be wrapped on the draw rolls.

While the illustrated embodiment utilizes a series of draw rolls forpurposes of drawing the yarn, it should be understood that any suitableprocess that can place a force on the yarn so as to elongate the yarnfollowing the quenching step can optionally be utilized. For example,any mechanical apparatus including nip rolls, godet rolls, steam cans,air, steam, or other gaseous jets can optionally be utilized to draw theyarn.

According to the embodiment illustrated in FIG. 1, following the yarndrawing step, the multifilament yarn 30 can be cooled and wound on atake-up roll 40. In other embodiments, however, additional processing ofthe yarn 30 may be carried out. For example, in one embodiment, themultifilament yarn can be subjected to a second draw. In general, asecond drawing step can be carried out at a higher temperature than thefirst draw. For instance, the heating element of the second drawing stepcan be heated to a temperature between about 10° C. and about 50° C.higher than the heating element of the first drawing step. In addition,a second draw can generally be at a lower drawing ratio that the firstdraw. For example, a second draw can be carried out at a draw ratio ofless than 5. In one embodiment, a second draw can be carried out at adraw ratio of less than 3. In the case of multiple draws, the total drawratio will be the product of each of the individual draws, thus a yarnfirst drawn at a draw ratio of 3, and then subsequently drawn at a drawratio of 2 will have been subjected to a total draw ratio of 6.

Optionally, the drawn multifilament yarn can be heat set. For example,the multifilament yarn can be relaxed or subjected to a very low drawratio (e.g., a draw ratio of between about 0.7 and about 1.3) andsubjected to a temperature of between about 130° C. and about 150° C.for a short period of time, generally less than 3 minutes. In someembodiment, a heat setting step can be less than one minute, forexample, about 0.5 seconds. This temperature can generally be higherthan the drawing temperature(s). This optional heat set step can serveto “lock” in the crystalline structure of the yarn following drawing. Inaddition, it can reduce heat shrinkage, which may be desired in someembodiments.

In another embodiment, the finished yarn can be surface treated toimprove certain characteristics of the yarn, such as wettability oradhesion, for example. For instance, the yarn can be fibrillated,subjected to plasma or corona treatments, or can include an addedsurface yarn sizing, all of which are generally known in the art, toimprove physical characteristics of the yarns. Beneficially, themultifilament yarns of the invention can have a high surface areaavailable for surface treatments, and thus can exhibit greatly improvedcharacteristics, such as adhesion, as compared to, for instance,monofilament fibers formed of similar materials.

In general, the finished multifilament yarn 30 can be wound on a spoolor take-up reel 40, as shown, and transported to a second location forformation of a secondary product. In an alternative embodiment, however,the multifilament yarn can be fed to a second processing line, where theyarn can be further processed to form a secondary product, such as awoven fabric, for example.

The polyolefin multifilament yarn of the present invention can generallyhave a drawn size of between about 0.5 denier per filament and about 100denier per filament. Beneficially, the disclosed multifilament yarn canhave a high tenacity and modulus, as measured in ASTM D2256-02, which isincorporated herein by reference, and as compared to other, previouslyknown multifilament polyolefin yarn. For example, the disclosedmultifilament yarn can have a tenacity greater than about 5grams/denier. In one embodiment, the multifilament yarn can have atenacity greater than about 7 grams/denier. In addition, themultifilament yarn of the present invention can have a high modulus, forexample, greater than about 100 grams/denier. In one embodiment, thedisclosed yarn can have a modulus greater than about 125 grams/denier,for example, greater than about 150 grams/denier, or greater than about200 grams/denier.

In addition, the disclosed yarn can exhibit relatively low elongationcharacteristics. For example, the multifilament yarn of the presentinvention can exhibit an elongation percentage of less than about 15%,as measured in ASTM D2256-02. In another embodiment, the yarn canexhibit less than about 10% elongation, for example, less than about 8%elongation.

The inventive multifilament yarns are also believed to possess a uniquecrystalline structure as compared to other, previously known polyolefinmultifilament yarns. There are several widely accepted means by which tomeasure molecular orientation in oriented polymer systems, among themscattering of light or X-rays, absorbance measurements, mechanicalproperty analysis, and the like. Quantitative methods include wide angleX-ray scattering (WAXS), and small angle X-ray scattering (SAXS).

Through the utilization of WAXS and SAXS techniques, the disclosedmultifilament yarns can be shown to be highly crystalline, highlyoriented, with little or no lamellar structure. In particular, thefilaments of the yarns can possess greater than about 80% crystallinityaccording to WAXS measuring techniques described below. For example,FIG. 3 illustrates the WAXS scattering pattern of a single filamentpulled from a multifilament yarn formed according to the presentlydisclosed process. In particular, the yarn (listed as sample Q in theExample section, below) was extruded through a spinneret with eightorifices of 0.012 inches diameter each, quenched in a water bath at 73°C., and drawn at a draw ratio of 16.2. The drawn yarn had a final denierof 406 grams/9000 m. As can be seen with reference to the Figure, where0φ is parallel to the yarn, the amorphous region of the disclosed yarnscan be 2θ from 10 to 30 and φ from 60 to 90 (the dark region near bottomof FIG. 3), and the crystalline region can be 2θ from 10 to 30 and φfrom −15 to 15 (including bright spots on the sides of FIG. 3). Thus byintegrating the x-ray scattering intensity in the crystalline andamorphous regions, the crystallinity of the filament can be obtained as

$\frac{\left( {I_{X} - I_{A}} \right)}{\left( I_{X} \right)}$where: I_(x) is the intensity in the crystalline region and I_(A) is theintensity in the amorphous region.

In addition, the polyolefin yarns of the invention can be highlyoriented, as shown by the narrow width of the WAXS peaks in FIG. 3.

FIG. 4 is the SAXS pattern of the filament shown in FIG. 3.Surprisingly, none of the expected structures relating to thecrystalline form, orientation, and amorphous regions appear in theFigure, and the yarn appears to have no true amorphous regions at all,but appears to be composed entirely of crystalline regions and highlyoriented amorphous regions.

SAXS patterns of multifilament yarns formed according to previously knowmethods generally include alternating crystalline and amorphous regionsas illustrated by bright spots of scattering intensity in the yarn axis.(See, for example, Polypropylene Fibers-Science and Technology, M.Ahmed, Elsevier Scientific Publishing Company, 1982, pp. 192-203, whichis incorporated herein by reference.) The positions of these spots canbe utilized to obtain the long period spacing between repeatingcrystalline regions. The absence of these spots in FIG. 4 indicates thatany amorphous regions in the inventive yarn of FIG. 4 have nearlyidentical electron density to the crystalline regions, and are thuscomposed of dense, highly oriented amorphous chains, or are absentaltogether. When combined with the WAXS pattern of FIG. 3, whichindicates that the amorphous intensity is at least 15%, it may beassumed that amorphous regions of the illustrated filament most likelyconsists of the highly oriented chains.

In addition, the equatorial scattering in SAXS patterns in generalarises from the center normal to the fiber axis and projects in a long,thin streak away from the center in each direction. In the inventiveyarns, and in further reference to FIG. 4, these equatorial scatteringstreaks have amplified greatly, to the point that they are more aptlydescribed as “wings.” This equatorial scattering arises fromfibrillation of the crystalline segments into more clearly definedneedle-like assemblies. A long equatorial streak arises from a highconcentration of cylindrical, shish-type structures in the yarn with thelamellae organized among or around the shishes, as “kabobs.” Thesestreaks generally appear in higher draw situations such as those of thepresent invention.

As can also be seen in FIG. 4, the filaments forming the yarns of thepresent invention under high draw conditions can describe a nearlyabsent meridonal reflection and an equatorial scattering that is strongsuch that the scattering ratio of equatorial to meridional scatteringintensity is high, but there remains strong density contrast asindicated by the overall intensity.

In general, the filaments forming the multifilament yarns of the presentinvention can have SAXS characteristics including a ratio of equatorialintensity to meridonal intensity of greater than about 1.0. In oneembodiment, this ratio can be greater than about 3. The filamentsforming the disclosed yarns can generally exhibit an equatorialintensity integrated from 2 θ of between about 0.4 to about 1.0 and φfrom about 60 to about 120 and from about 240 to about 300 (zero φ beingparallel to the yarn, or vertical in reference to FIG. 4). In addition,the yarns can exhibit a meridonal intensity integrated from 2 θ ofbetween about 0.4 and about 1.0 and φ from about −60 to about 60 andfrom about 120 to about 240.

The disclosed multifilament polyolefin yarns can be beneficiallyutilized in many applications. For example, the high strength and hightenacity of the disclosed yarns can provide them with excellentqualities for utilization in any application suitable for previouslyknown multifilament polyolefin yarns. For example, in certainembodiments, the disclosed yarns can be beneficially utilized asreinforcement material in a matrix. For example, in one embodiment,following formation of the multifilament drawn yarn according to thedisclosed processes, the yarn can be further processed so as to besuitable for use as a reinforcement material in a matrix. For Instance,the multifilament yarns of the present invention can be chopped,fibrillated, flattened or otherwise deformed as is generally known inthe art. As the multifilament yarns are processed in order to form thedisclosed reinforcement materials, the multifilament yarns can not onlybe shortened, deformed, abraded, and the like, but in addition, themultifilament yarns can become shredded. That is, during processing,individual filaments of the yarns can become separated from one anotherin forming the disclosed reinforcement materials.

Accordingly, in one embodiment, the present invention is directed toreinforcement materials formed of the disclosed yarns. In particular,the reinforcement materials of the present invention can includechopped, shredded, and/or degraded yarns as herein described. Ingeneral, the reinforcement materials can include relatively shortlengths of the multifilament yarns and/or individual filaments that havebeen shredded off of the formed multifilament yarns. For example, thereinforcement materials of the present invention can generally be lessthan about 5 inches in length. In one embodiment, the reinforcementmaterials can be less than about 3 inches in length, for instance, lessthan about 1 inch in length,

During use, the reinforcement materials of the disclosed invention canbe combined with a matrix material such as adhesives, asphalt, plastics,rubber, or hydratable cementitious compositions including ready-mix orpre-cast concrete, masonry concrete, shotcrete, bituminous concrete,gypsum compositions, cement-based fireproofing compositions, and thelike.

In one embodiment of the present invention, the disclosed yarns can befurther processed if necessary and utilized in forming secondaryproducts including those products that in the past have been formed withpreviously known multifilament polyolefin yarns. For example, thedisclosed yarns can be utilized in forming ropes, and woven or nonwovenfabrics such as may be found in machinery belts or hoses, roofingfabrics, geotextiles, and the like. In particular, the disclosedmultifilament yarns can be suitable for use in forming a secondaryproduct according to any known technique that has been used in the pastwith previously known polyolefin multifilament yarns. Due to theimproved physical properties of the disclosed yarns, however, andparticularly, the higher modulus and tenacity of the disclosed yarns,secondary products formed utilizing the inventive yarns can provideimproved characteristics, such as strength and tenacity, as compared tosimilar products formed of previously known multifilament polyolefinyarns.

The invention may be better understood with reference to the followingExample.

EXAMPLE

Yarn samples were formed on system similar to that illustrated inFIG. 1. In particular, the system included a ¾ inch, 24:1 single screwextruder with three temperature zones, a head with a melt pump andspinneret, a liquid quench tank (40 inch length), with two rollers inthe tank, a vacuum water removal system, a spin finish applicator, threeheated godet rolls, a forced air oven (120 inch length) and a Leesona®winder.

Materials utilized in forming the yarns included Atofina® 3462, apolypropylene homopolymer with a melt flow index of 3.7 and Atofina®3281, a polypropylene homopolymer with a melt flow index of 1.3 (bothavailable from ATOFINA Petrochemicals, Inc. of Houston, Tex.), a 10%concentrate of a nucleating agent composition, specifically Millad® 3988(3,4-dimethyl dibenzylidiene sorbitol) in a 12 MFI polypropylenehomopolymer (available from Standridge Color Corporation, Social Circle,Ga., USA), and a polyethylene homopolymer with a melt flow index of 12(available from TDL Plastics, of Houston, Tex.).

Table 1, below, tabulates the formation conditions of 37 differentsamples including the material make-up (including the polymer used andthe total weight percent of the nucleating agent in the melt), thespinneret hole size in inches, the total number of filaments extruded,the temperature of the quench water bath, the roll speeds of the drawingrolls, the total draw ratio (Roll 3/Roll 1), and the temperature of thedrawing oven. In addition, as the nucleating agent is provided in a 10%concentrate composition of the nucleating agent in a 12 MFIpolypropylene homopolymer, the material make-up of those samples thatinclude an amount of a nucleating agent will also include an amount ofthe 12 MFI polypropylene homopolymer from the concentrate. For example,a sample that is listed as containing FINA 3462/0.2% Millad will contain0.2 wt % of the nucleating agent, 1.8 wt % of the 12 MFI polypropylenehomopolymer used in forming the 10% nucleating agent composition, and 98wt % of the FINA 3462 3.7 MFI polypropylene homopolymer.

TABLE 1 Spinneret Water Oven Hole Size # Fils Temp Roll 1 Roll 2 Roll 3T Sample Material inches # C. m/min m/min m/min DR ° C. A Fina 3462 0.041 25 11.3 100 110 9.7 120 B Fina 3462/0.2% Millad 0.04 1 25 8 123 12315.4 140 C Fina 3462/0.2% Millad 0.027 17 25 5 30 30 6.0 120 D Fina3462/0.2% Millad 0.027 17 25 5 37.5 37.5 7.5 150 E Fina 3462/0.25%Millad 0.018 1 25 10.5 135 135 12.9 130 F Fina 3462/0.25% Millad 0.018 825 9 85 85 9.4 130 G Fina 3462/0.25% Millad 0.018 8 25 6 85 85 14.2 130H Fina 3462/0.25% Millad 0.012 8 25 8.75 85 85 9.7 130 I Fina 3462/0.25%Millad 0.012 8 25 9.5 85 85 8.9 130 J Fina 3462/0.20% Millad 0.012 8 258 85 85 10.6 130 K Fina 3462/0.20% Millad 0.012 8 25 6.25 85 85 13.6 130L Fina 3462/0.20% Millad 0.012 8 25 5.5 85 85 15.5 130 M Fina 3462/0.20%Millad 0.012 8 25 5.5 85 85 15.5 130 N Fina 3462/0.20% Millad 0.012 5 255 85 85 17.0 130 O Fina 3462/0.20% Millad 0.012 5 55 6 85 85 14.2 130 PFina 3462/0.20% Millad 0.012 5 55 6 85 85 14.2 130 Q Fina 3462/0.20%Millad 0.012 8 73 5.25 84 85 16.2 130 R Fina 3462/0.20% Millad 0.012 885 5.5 84 85 15.5 130 S Fina 3462/0.20% Millad 0.012 8 85 5.25 84 8516.2 130 T Fina 3462/0.20% Millad 0.012 8 82 4.75 84 85 17.9 145 U Fina3462/0.20% Millad 0.012 8 82 4.6 84 85 18.5 150 V Fina 3281/0.2% Millad0.012 8 75 4.5 84 85 18.9 140 W Fina 3281/0.2% Millad 0.012 8 75 4.5 8485 18.9 140 X Fina 3281 0.012 8 75 6 84 85 14.2 130 Y Fina 3281 0.012 875 4.5 84 85 18.9 140 Z Fina 3281 0.012 8 75 4.25 84 85 20.0 140 AA Fina3281 w/5% 12 MFI PE 0.012 8 75 5 84 85 17.0 130 BB Fina 3281/0.2% Millad0.012 8 75 4.75 84 85 17.9 150 CC Fina 3281/0.2% Millad 0.012 8 75 4.2584 85 20.0 140 DD Fina 3281/0.2% Millad 0.012 8 75 4 84 85 21.3 140 EEFina 3281/0.2% Millad 0.012 8 75 4 84 85 21.3 140 FF Fina 3281/0.2%Millad 0.012 8 75 4 84 85 21.3 140 GG Fina 3281/0.2% Millad 0.012 8 75 584 85 17.0 140 HH Fina 3281/0.2% Millad 0.012 8 75 4.75 84 85 17.9 140II Fina 3281/0.2% Millad 0.008 20 75 4.25 84 85 20.0 140 JJ Fina3281/0.2% Millad 0.008 20 75 5.5 84 85 15.5 150 KK Fina 3281/0.2% Millad0.008 20 75 4.25 84 85 20.0 140

Following formation, the samples were tested for a number of physicalproperties including denier, denier per filament, elongation, tenacity,modulus, and toughness, all according to ASTM D2256-02, previouslyincorporated by reference. Results are shown below in Table 2.

TABLE 2 Denier Den/fil Elong Ten Mod Tuff Sample Material g/9000 mg/9000 m % g/d g/d g/d A Fina 3462 302 302 24 5.2 60 B Fina 3462/0.2%Millad 292 292 8 5.9 107 C Fina 3462/0.2% Millad 1300 76 21 5.5 50 DFina 3462/0.2% Millad 1414 83 16 4.2 43 E Fina 3462/0.25% Millad 63 6310 7.9 125 F Fina 3462/0.25% Millad 293 37 22 8.5 G Fina 3462/0.25%Millad 532 67 11.7 10.4 173 H Fina 3462/0.25% Millad 210 26 16.9 8.1 100I Fina 3462/0.25% Millad 161 20 14.8 7.2 100 J Fina 3462/0.20% Millad222 28 15.0 9.0 108 K Fina 3462/0.20% Millad 316 40 9.1 8.4 154 L Fina3462/0.20% Millad 362 45 8.9 8.8 159 M Fina 3462/0.20% Millad 420 5311.2 9.6 146 N Fina 3462/0.20% Millad 297 59 10.4 10.5 171 O Fina3462/0.20% Millad 287 57 11.3 9.4 144 P Fina 3462/0.20% Millad 276 559.2 7.7 132 Q Fina 3462/0.20% Millad 406 51 9.3 11.6 207 R Fina3462/0.20% Millad 369 46 14.0 8.2 S Fina 3462/0.20% Millad 390 49 14.08.4 T Fina 3462/0.20% Millad 345 43 9.3 10.4 189 U Fina 3462/0.20%Millad 324 41 8.8 10.9 201 V Fina 3281/0.2% Millad 353 44 7.3 9.3 185 WFina 3281/0.2% Millad 358 45 6.9 9.7 203 X Fina 3281 329 41 12.5 9.3 1310.75 Y Fina 3281 301 38 10.7 10.3 160 0.73 Z Fina 3281 316 40 9.7 9.8165 0.66 AA Fina 3281 w/5% 12 MFI PE 328 41 14.0 8.9 BB Fina 3281/0.2%Millad 270 34 9.1 8.5 159 0.62 CC Fina 3281/0.2% Millad 287 36 8.6 8.9181 0.58 DD Fina 3281/0.2% Millad 265 33 8.9 10.4 203 0.68 EE Fina3281/0.2% Millad 364 46 8.1 9.1 178 0.61 FF Fina 3281/0.2% Millad 403 506.5 8.5 181 0.41 GG Fina 3281/0.2% Millad 356 45 8.4 10.3 200 0.60 HHFina 3281/0.2% Millad 375 47 5.3 8.8 203 0.39 II Fina 3281/0.2% Millad396 20 6.4 8.3 178 0.46 JJ Fina 3281/0.2% Millad 589 29 9.6 9.2 166 0.65KK Fina 3281/0.2% Millad 423 21 6.1 7.8 178 0.47X-Ray Scattering Analysis

The samples were studied by small angle x-ray scattering (SAXS). TheSAXS data were collected on a Bruker AXS (Madison, Wis.) Hi-Starmulti-wire detector placed at a distance of 105.45 cm from the sample inan Anton-Paar vacuum. X-rays (λ=0.154178 nm) were generated with aMacScience rotating anode (40 kV, 40 mA) and focused through threepinholes to a size of 0.2 mm. The entire system (generator, detector,beampath, sample holder, and software) is commercially available as asingle unit from Bruker AXS. The detector was calibrated permanufacturer recommendation using a sample of silver behenate.

A typical SAXS data collection was conducted as follows: A polypropylenefilament bundle was wrapped around a holder, which was placed in thex-ray beam inside an Anton-Paar vacuum sample chamber on the x-rayequipment. The sample chamber and beam path was evacuated to less than100 mTorr and the sample was exposed to the X-ray beam for between about45 minutes and one hour. Two-dimensional data frames were collected bythe detector and unwarped automatically by the system software.

An analysis of the scattered intensity distribution (2θ=0.2°-2.5°) intothe equatorial or meridonal directions was calculated from the raw dataframes by dividing the scattering into 2 regions: an equatorialscattering region, integrated from 2 θ of between about 0.4 to about 1.0and φ from about 60 to about 120 and from about 240 to about 300 (zero φbeing parallel to the yarn, or vertical in FIG. 4), and the meridonalscattering region, integrated from 2 θ of between about 0.4 and about1.0 and φ from about −60 to about 60 and from about 120 to about 240.Total counts were summed for each of the two regions and the ratiocalculated and tabulated for each sample in Table 3, below.

TABLE 3 Meridional Equatorial Scattering Scattering Equatorial/ SampleMaterial counts counts Meridional A Fina 3462 150499 18174 0.12 B Fina3462/0.2% 83716 293818 3.51 Millad C Fina 3462/0.2% 125348 20722 0.17Millad D Fina 3462/0.2% 169657 37642 0.22 Millad E Fina 3462/0.25% 57067265606 4.65 Millad F Fina 3462/0.25% 28192 23494 0.83 Millad G Fina3462/0.25% 34164 182207 5.33 Millad H Fina 3462/0.25% 14203 11505 0.81Millad I Fina 3462/0.25% 21722 17758 0.82 Millad J Fina 3462/0.20% 3626474971 2.07 Millad K Fina 3462/0.20% 82734 662846 8.01 Millad L Fina3462/0.20% 47815 175599 3.67 Millad M Fina 3462/0.20% 53247 323136 6.07Millad N Fina 3462/0.20% 89254 561719 6.29 Millad O Fina 3462/0.20%52212 313477 6.00 Millad P Fina 3462/0.20% 57344 365467 6.37 Millad QFina 3462/0.20% 107220 401479 3.74 Millad R Fina 3462/0.20% 40419 591631.46 Millad S Fina 3462/0.20% 48712 106876 2.19 Millad T Fina 3462/0.20%49098 153474 3.13 Millad U Fina 3462/0.20% 65459 210907 3.22 Millad VFina 3281/0.2% 54222 220056 4.06 Millad W Fina 3281/0.2% 43058 2570975.97 Millad X Fina 3281 53060 159811 3.01 Y Fina 3281 57218 210415 3.68Z Fina 3281 45224 186045 4.11 AA Fina 3281 w/5% 35826 87938 2.45 12 MFIPE BB Fina 3281/0.2% 37907 98972 2.61 Millad CC Fina 3281/0.2% 54109164494 3.04 Millad DD Fina 3281/0.2% 47656 202256 4.24 Millad EE Fina3281/0.2% 51026 171581 3.36 Millad FF Fina 3281/0.2% 48872 181346 3.71Millad GG Fina 3281/0.2% 49382 282585 5.72 Millad HH Fina 3281/0.2%54467 348671 6.40 Millad II Fina 3281/0.2% 57703 260487 4.51 Millad JJFina 3281/0.2% 52353 178923 3.42 Millad KK Fina 3281/0.2% 46881 2032814.34 Millad

As can be seen with reference to Table 3, while the disclosed materialscan in some cases give to rise to a SAXS scattering profile with bothmeridonal scattering and equatorial scattering, the meridionalscattering is low compared to the highly unique strong equatorialscattering giving rise to a high ratio of equatorial scattering tomeridional scattering. At the very least, then, the presence of intensescattering wings in the equatorial direction provides the desiredcrystal structures that impart the properties of high tenacity and highmodulus found in the multifilament yarns.

It will be appreciated that the foregoing examples, given for purposesof illustration, are not to be construed as limiting the scope of thisinvention. Although only a few exemplary embodiments of this inventionhave been described in detail above, those skilled in the art willreadily appreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention that isdefined in the following claims and all equivalents thereto. Further, itis recognized that many embodiments may be conceived that do not achieveall of the advantages of some embodiments, yet the absence of aparticular advantage shall not be construed to necessarily mean thatsuch an embodiment is outside the scope of the present invention.

1. A melt-spun drawn multifilament yarn comprising at least threefilaments, each filament including a polypropylene and each filamenthaving a denier of less than about 300 grams/9000 meters, the melt-spundrawn multifilament yarn having been drawn at a draw ration of greaterthan about 6 and the melt-spun drawn multifilament yarn having a modulusgreater than about 100 grams/denier, and wherein at least one of saidfilaments has a ratio of equatorial intensity to meridonal intensitygreater than about 3.0 according to SAXS measuring techniques.
 2. Themelt-spun drawn multifilament yarn of claim 1, wherein the yarn has atenacity greater than about 5 grams/denier.
 3. The melt-spun drawnmultifilament yarn of claim 1, wherein each filament has a denier ofbetween about 0.5 grams/9000 meters and about 100 grams/9000 meters. 4.The melt-spun drawn multifilament yarn of claim 1, wherein the yarn hasa modulus greater than about 150 grams/denier.
 5. The melt-spun drawnmultifilament yarn of claim 1, wherein the yarn has a tenacity greaterthan about 7 grams/denier.
 6. The melt-spun drawn multifilament yarn ofclaim 1, wherein the yarn exhibits an elongation of less than about 10%.